1. Field of the Invention
The integration of slab width has a remarkable merit in energy-saving based on the intensification of continuously casting molds in the continuous casting operation and the shortening of steps. Recently, the continuous casting is synchronized with a hot strip mill by unifying widths of continuously cast slabs.
In order to unify the slab width, it is necessary that the width of the slab can largely be reduced up to a minimum product width at a hot rough rolling process as a preliminary step. A method of reducing slab width, which satisfies the above requirement, will be described below.
2. Related Art Statement
There is known a method of largely reducing slab width through a large-size roll or large-size caliber roll, which has been developed from the conventional width reducing method through a vertical roll mill as a width reducing adjustment.
In this method, however, the slab is largely reduced by the roll, so that metal flows particularly at the leading and tail ends of the width-reduced slab toward these leading and tail ends, and consequently a so-called crop largely grows to extremely degrade the yield.
On the other hand, Japanese Patent laid open No. 59-101,201 has proposed a continuously widthwise pressing, wherein a slab is fed between a pair of press tools approaching to and separating from each other at a predetermined minimum opening to gradually reduce the width of the slab between the slant portions of the press tools and make the slab to a given slab width between the parallel portions of the press tools. Particularly, Japanese Patent laid open No. 61-135,402 discloses that in order to minimize the leading end crop, the quantity of the leading end portion of the slab fed between the press tools is larger than the quantity of the steady portion, and in order to prevent the dull deformation of the slab at its leading end shoulder, the leading end portion of 50.about.100 mm in length is wider than the width of the steady portion.
When the thus treated slab is rolled to produce a hot strip coil, the dull deformation of the shoulder portion is prevented and the crop loss becomes small, but there is caused another problem that the strip width is largely shortened at a position located inward from the leading end. Such a narrow width portion is particularly large at the leading end side and also may be caused at the tail end side, which is cut out as a width shortage to largely reduce the yield.